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Hydrodynamic Approach (hydrodynamic + approach)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Hydrodynamic modelling of cometary particles captured in aerogel and the Earth's atmosphere

METEORITICS & PLANETARY SCIENCE, Issue 10 2009
S. G. Coulson
We present a simplified model for the formation of the tracks formed in aerogel by hypervelocity impacts of cometary material. Using a hydrodynamic approach to model this class of problem overcomes some of the errors associated with previous semi-analytical models for track formation (Coulson 2009). The hydrodynamic models developed allow the particle velocity, temperature and pressure to be calculated as a function of track length within aerogel. A qualative description of how this model can be extended to the formation of bulbous cavities using the Chapman-Jouquet theory is provided. [source]

Experimental and theoretical investigation of terahertz optical-beating detection by plasma waves in high electron mobility transistors

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008
H. Marinchio
Abstract A photomixed laser beam of two 1.55 mm cw lasers is used to obtain interband photoexcitation at the difference frequency and at room temperature in submicron gate-length InAlAs/InGaAs transistors. Results show the clear excitation of plasma oscillation modes in the transistor channel. Fundamental plasma resonant frequency and its odd harmonics can be tuned with the applied gate voltage. Numerical simulations have also been performed using a hydrodynamic approach coupled to a pseudo-2D Poisson equation. Numerical results are in qualitative agreement with experiments and confirm optical beating detection at terahertz frequencies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

RNAi-mediated reversible opening of the blood-brain barrier

THE JOURNAL OF GENE MEDICINE, Issue 8 2008
Matthew Campbell
Abstract Background The blood-brain barrier (BBB) contains tight junctions (TJs) which reduce the space between adjacent endothelial cells lining the fine capillaries of the microvasculature of the brain to form a selective and regulatable barrier. Methods Using a hydrodynamic approach, we delivered siRNA targeting the TJ protein claudin-5 to the endothelial cells of the BBB in mice. Results We have shown a significant decrease in claudin-5 mRNA levels 24 and 48 hours post-delivery of siRNA, with levels of protein expression decreasing up to 48 hours post-injection compared to uninjected, phosphate-buffered saline (PBS)-injected and non-targeting siRNA-injected mice. We observed increased permeability at the BBB to molecules up to 742 Da, but not 4400 Da, using tracer molecule perfusion and MRI analysis. To illustrate the functional efficacy of size-selective and transient barrier opening, we have shown that enhanced delivery of the small neuropeptide thyrotropin-releasing hormone (TRH) (MW 360 Da) to the brains of mice 48 hours post-injection of siRNA targeting claudin-5 significantly modifies behavioural output. Conclusions These data demonstrate that it is now possible to transiently and size-selectively open the BBB in mice, allowing in principle the delivery of a wide range of agents for the establishment and treatment of experimental mouse models of neurodegenerative, neuropsychiatric and malignant diseases. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Calculation of profile of charge carrier concentration in modulation doped structure with a wide potential well

ANNALEN DER PHYSIK, Issue 12 2009
L.Yu. Shchurova
Abstract We investigate the equilibrium state of interacting electron system with Fermi statistics in modulation doped structure with a wide quantum well. The model is formulated for the carrier system with a sufficiently high density, such that the de Broglie wavelength of electrons is smaller than the width of the quantum well. Due to a significant interaction of electrons with electric field of the doped layer, a state with strongly-inhomogeneous density of electrons is formed. Within the hydrodynamic approach, we set up formalism for calculating the electron density across the width of the potential well. We have obtained the exact solution of the equations, which is expressed in terms of hypergeometric functions. Based on the deduced formulas, we performed numerical computations for the profile of carriers' concentrations in a potential well in the modulation doped Si/SiGe/Si structures. [source]